I
[IK89] Neil Immerman and Dexter C. Kozen. Definability with Bounded Number of Bound Variables. Information and Computation 83(2):121-139. Academic Press, November 1989. 
@article{icomp83(2)-IK,
  author =              {Immerman, Neil and Kozen, Dexter C.},
  title =               {Definability with Bounded Number of Bound Variables},
  publisher =           {Academic Press},
  journal =             {Information and Computation},
  volume =              {83},
  number =              {2},
  pages =               {121-139},
  year =                {1989},
  month =               nov,
}
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